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Showing papers on "Friedmann–Lemaître–Robertson–Walker metric published in 1985"


Journal ArticleDOI
TL;DR: In this paper, a cosmological model consistent with the large number hypothesis (LNH) with Einstein's theory of gravitation is proposed, and a tentative generalization of Einstein's field equations with time-dependent cosmologically and gravitational constants is proposed.
Abstract: In an attempt to reconcile the large number hypothesis (LNH) with Einstein's theory of gravitation, a tentative generalization of Einstein's field equations with time-dependent cosmological and gravitational constants is proposed. A cosmological model consistent with the LNH is deduced. The coupling formula of the cosmological constant with matter is found, and as a consequence, the time-dependent formulae of the cosmological constant and the mean matter density of the Universe at the present epoch are then found. Einstein's theory of gravitation, whether with a zero or nonzero cosmological constant, becomes a limiting case of the new generalized field equations after the early epoch.

72 citations


Journal ArticleDOI
TL;DR: In this article, two families of cosmological solutions are presented in D = 6, N = 2 Kaluza-Klein supergravity theories, and all solutions in the latter family approach the Friedmann universe asymptotically.

62 citations


Journal ArticleDOI
TL;DR: In this article, the power law, oscillatory and exponential behavior for the D-dimensional Einstein-Maxwell, N = 2, D = 10 and N = 1,D = 11 supergravity models were studied.

50 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that shear-free expanding irrotational perfect fluids obeying a barotropic equation of state p = p(μ) and satisfying the field equations of general relativity form three distinct classes.
Abstract: In an earlier investigation of the class of shear‐free expanding (or contracting) irrotational perfect fluids obeying a barotropic equation of state p=p( μ), and satisfying the field equations of general relativity, it was shown that the space‐times form three distinct classes. In one class, the fluid acceleration is zero (i.e., the flow is geodesic), and the space‐times are the well‐known spatially homogeneous and isotropic Friedmann–Robertson–Walker (FRW) models. In the other two classes, the acceleration is nonzero, and the space‐times are spatially anisotropic and are less familiar. One of these classes consists of the spherically symmetric Wyman solutions, whereas models that are plane symmetric, and either spatially or temporally homogeneous, constitute the final class. Analytic forms for these anisotropic space‐time metrics were given, although in each case their exact determination would depend upon the solution of a single nonlinear ordinary differential equation, which has not been achieved. The...

38 citations


Journal ArticleDOI
TL;DR: In this paper, perfect fluid solutions of the Einstein field equations are presented in which the geometrical part is formally identical to the k = 0, R(t) = t/sup 1/2/ radiation-like FRW line element.
Abstract: Imperfect fluid solutions of the Einstein field equations are presented in which the geometrical part is formally identical to the k = 0, R(t) = t/sup 1/2/ radiation-like FRW line element. These exact solutions include some which are self-similar.

21 citations


Journal ArticleDOI
TL;DR: In this article, a new class of inhomogeneous and anisotropic cosmologies on the assumption of a fluid not in the thermal equilibrium state as the source of curvature was obtained.

12 citations


Journal ArticleDOI
TL;DR: The class of anisotropic and inhomogeneous cosmological solutions of the Einstein field equations with a perfect fluid source obeying an equation of state p = ..gamma…rho, 0<..gamma..
Abstract: The class of anisotropic and inhomogeneous cosmological solutions of the Einstein field equations with a perfect fluid source obeying an equation of state p = ..gamma..rho, 0<..gamma..

11 citations


Journal ArticleDOI
TL;DR: In this paper, a non-static exact solution of the Einstein equations corresponding to a conformally invariant scalar field with trace-free energy momentum tensor is obtained for the Robertson-Walker type metric.
Abstract: A non-static exact solution of the Einstein equations corresponding to a conformally invariant scalar field with trace-free energy momentum tensor is obtained for the Robertson-Walker type metric. Some physical properties of the solution are discussed.

7 citations


Journal ArticleDOI
TL;DR: A general procedure for calculating the particle number density with any isotropically contracting compact space is developed and the number density is calculated to lowest order in perturbation theory when the compactspace is T/sup n/ and examples are given.
Abstract: Particle production due to a conformally coupled scalar field plus gravity in n+4 dimensions is considered. The metric for the gravitational field is taken to be a generalization of a Robertson-Walker metric. A general procedure for calculating the particle number density with any isotropically contracting compact space is developed. The number density is then calculated to lowest order in perturbation theory when the compact space is T/sup n/ and examples are given.

7 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the quark-hadron transition in a cosmological anisotropic framework and found a general form for the expansion law in the actual phase transition: it deviates from a "radiative" behaviour as in a FRW model.

3 citations


Journal ArticleDOI
TL;DR: In this article, the two-loop contributions to the induced cosmological constant are computed in a matterless Einstein theory of gravity expanded about a Minkowski background with no cosmology term present in the classical action.

Journal ArticleDOI
TL;DR: An exact solution of the Einstein field equations for a combination of black-body radiation and an imperfect fluid, in which the geometrical background is a flat FRW metric, is presented in this article.

Journal ArticleDOI
TL;DR: In this paper, the evolutionary behavior of the universe during the radiation-dominated and matter-dominated eras is examined within the framework of a cosmological model with a time-dependent cosmology constant.
Abstract: Within the framework of a cosmological model with a time-dependent cosmological constant Λ, we examine the evolutionary behaviour of the Universe during the radiation-dominated and matter-dominated eras. The smallness of the cosmological constant and the origin of galaxy formation are explained. For a dust-filled universe withp≃0, the model yields a cosmological solutionk=−1,R∼t. The relationship among Einstein equivalence principle, Mach's principle and Dirac's principle is also elucidated through the time-dependent Λ. It is shown that these principles are compatible, and Mach's principle and Dirac's principle can be viewed as an initial-value condition and a dynamic consequence of Einstein's equations (satisfying Einstein equivalence principle), respectively.

Journal ArticleDOI
TL;DR: In this paper, a theory of a gauged gravitational field with localization of the group of motions of a homogeneous static Einstein universe (Einstein group R x SO(4)) is formulated.
Abstract: A theory of a gauged gravitational field with localization of the group of motions of a homogeneous static Einstein universe (Einstein group R x SO(4)) is formulated. Starting from the tetradic components of Einstein's universe, a relationship is established between the Riemannian metric and the gauge fields of Einstein's group. The metric connection with torsion, transforming when the gauge fields are switched off into the Christoffel connection of Einstein's universe, is found. It is shown that in the limit of infinite radius of curvature of Einsteinr's universe, the given Einstein-invariant gauge theory transforms into the tetradic theory of gravitation with localized triadic rotations. Exact solutions are obtained in the form of nonsingular cosmological models.

Journal ArticleDOI
TL;DR: In this paper, the same authors considered the same problem with single-loop quantum corrections describing the vacuum polarization of physical fields and showed that in the interval of times in which only the singleloop corrections are important for the strong classical gravitational field these equations give a unique stable solution of Friedmann type for the cosmological problem.
Abstract: The Einstein equations with single-loop quantum corrections describing the vacuum polarization of physical fields are considered. It is shown that in the interval of times in which only the single-loop corrections are important for the strong classical gravitational field these equations give a unique stable solution of Friedmann type for the cosmological problem.

Journal ArticleDOI
TL;DR: In this article, the authors calculated the perturbations in the energy level of the hydrogen atom in the four states 1S 1 2, 2S 2 2 2P 3 2 and 2P 1 2 2, caused by the background curvature of the Robertson-Walker metric.

Book ChapterDOI
01 Jan 1985
TL;DR: In this paper, conditions under which the Einstein equations behave like linear equations were established, in the sense that the sum of an exact and an approximate solution is a new exact solution, and superposition theorems were obtained for the vacuum Einstein equations with and without cosmological constant, the coupled Einstein-Maxwell equations, and the Einstein equation for a perfect fluid.
Abstract: Conditions are established under which the Einstein equations of General Relativity behave like linear equations in the sense that the sum of an exact and an approximate solution is a new exact solution. Superposition theorems are obtained for the vacuum Einstein equations with and without cosmological constant, the coupled Einstein-Maxwell equations, and the Einstein equations for a perfect fluid.